A mobile communication network is typically used to provide network services for a user equipment within the mobile communication network. For example, the network services being provided by the mobile communication network may be voice call services, short message services (SMS) and/or data services. The network services are provided to the user equipment—which may also be called a terminal or mobile device—when the user equipment is registered and subsequently attached to the mobile communication network. The mobile communication network serving the user equipment may also be called a cellular network or serving network.
During the registration procedure, the serving network may have to verify that the terminal—as identified by its subscriber identity module (SIM) card credentials—possesses a subscription. The information pertinent to a subscription is stored in a home subscriber server (HSS), and contains not only the subscriber identification but also numerous service related parameters applicable to the subscription. The totality of this information may be called a subscription profile. Based on the network cell being used by the user equipment during the registration procedure, the serving network selects a serving core network node having a functionality—for example a visitor location register (VLR) functionality in case of a mobile-services switching center (MSC)—that, among other functions, enables the serving core network node to download a local copy of the relevant part of the subscription profile from the home subscriber server (HSS) for local processing. Thereby, the local copy of the subscription profile is used by the serving core network node to make service-related decisions when the terminal invokes a service—for example starting a voice call without having to contact the home subscriber server (HSS) every time a service is invoked. Moreover, the serving core network node may be used to maintain the terminal's location within the network and/or report specific changes in the local copy of the subscription profile to the home subscriber server (HSS), wherein the specific changes may also include a change of the serving core network node.
Typically, the subscription profile is stored in a home subscriber server (HSS) of the subscriber's home network. The home subscriber server (HSS) may also be called a home location register (HLR). With regard to the registration of the user equipment to the serving core network node, a non-roaming case may be distinguished from a roaming case. In the non-roaming case, the serving network is the home network of the subscriber associated with the user equipment. This means that the user equipment is registered at the serving core network node of the subscriber's home network, wherein the serving core network node retrieves the subscription profile related to the subscriber from the home subscriber server (HSS) within the subscriber's home network. In contrast, the roaming case relates to a situation in which an inbound roamer (i.e. a roaming subscriber from a foreign network) is registered at the serving core network node of the serving network, wherein the serving network and the home network are different networks.
In the roaming-case, the serving core network node has to retrieve the subscriber profile from the foreign home subscriber server (HSS) within the subscriber's home network. Thus, the serving core network node must be technically enabled to identify the inbound roamer's home network, and to communicate with the home network's home subscriber server (HSS). However, the serving core network node typically may not always have all the information about the home network's home subscriber server (HSS) design required to successfully register and attach the inbound roamer to the serving network. Furthermore, only a global route to a roaming gateway in the home network may be provided such that it is the home network's responsibility to locate the proper homer subscriber server (HSS).
Thus, roaming services are typically provided for a user equipment within the serving network by configuring both networks—i.e. the subscriber's home network and the serving network—such that all serving core network nodes of the serving network are enabled to communicate with the home network of each and every inbound roamer. However, this might lead to situations in which the provider of the serving network may be unable to guarantee that the involved nodes of both the home network and the serving network are configured to use interoperable versions of the communication protocol at all times. Therefore, relatively complex technical efforts are required to provide a working communication between all serving core network nodes of the serving network and the home subscriber servers of a plurality of foreign networks. This might be particularly relevant, when the serving network and home network use different standards according to different specification releases and/or when the home network is updated to a newer specification release.